A new cardiac valve fabricated from a novel polyurethane material has been fabricated and tested in vitro. These preliminary tests indicate that this device is durable (no failures in tests lasting at least 200 million cycles) and possesses hemodynamic characteristics comparable to currently available valves. The segmented polyurethaneurea developed for this use is unique because its bulk properties, for long-term durability, and surface properties, for biocompatibility, have been separated and developed in two distinct materials. Blending of the two components results in a single material incorporating the properties of each. In vivo evaluation of rods of this material and of ventricular assist device pumping sacs has demonstrated its excellent physical and thromboresistant characteristics. We propose to fabricate valves and test them both in vitro and in vivo. Steady-state and pulsatile conditions will be used for the mock loop testing. Valves will be implanted in left ventricle to aorta shunts in calves, a model that we have used many times to evaluate other devices. Additional hemodynamic testing will be performed on explanted valves, as will SEM and X-ray analysis.